Oftentimes, when a mass is subject to pulling or holding actions, it is advantageous to compensate, at least partially, for the acting tractive forces.
For example, German utility model DE 201 12 750 U1 describes a cable rewind device for power-related garden and outdoor equipment that possesses a cable drum for rewinding a cable. The cable drum is subject to the load of a mainspring in the direction in which the cable is rewound. When the cable is unwound from the cable drum, the mainspring is tensioned. As a result, the cable unwound from the cable drum is constantly subject to a pulling force. This pulling force causes the cable to run in a straight direction from the electrically driven machine toward the cable collector. The cable collector can be mounted above the area to be operated on by the electrical machine (e.g., on a house wall). In the event of a breakage of the mainspring, it would be desirable for the cable collector to be blocked so that no more cable is released.
In another example, German patent specification DE 197 47 393 C2 describes a weight compensating apparatus that can be used for a medical device. The weight compensating apparatus has a cable drum that can be subjected to the force of a spiral spring element. The cable drum can receive a supporting cable capable of bearing a payload and has a safety device for triggering a locking device in the event that the spiral spring element breaks. Upon breakage of the spiral spring element, the outer end of the spiral spring element engages with a pawl of the locking device, which can be subjected to the force of a pawl spring in order to inhibit adjustability of the cable drum. The force of the pawl spring is such that the pawl does not release the locking of the cable drum during tensioning of the spiral spring element until a specific force is reached.
It has been found that a spring breakage pawl used as a safety device does not respond consistently in every fault situation. Although the safety device triggers momentarily under unfavorable conditions, it does not remain reliably pressed outward.
In short, it would be desirable to safely move a payload in an upward direction in the event of a broken spring. However, conventional approaches to solving this problem typically necessitate the application of considerable force.